Electropolymerization of glutaraldehyde observed by scanning tunneling microscopy and its implications for scanning tunneling microscopy imaging of organic material

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Abstract
Here we show an example of scanning tunneling microscopy triggering and subsequently investigating a chemical reaction on a nanometer scale. It is observed that applying a high electric field to a graphite substrate homogeneously coated with a thin film of glutaraldehyde causes the glutaraldehyde molecules to form clusters ranging from 5 to 15 molecules in size. Studies on the lateral distribution of the clusters suggest that a lateral flux of charge between the negatively biased tip and the grounded substrate causes a type of electropolymerization of these molecules. We believe that a significant current flows due to charged species which have been created by the primary tunneling electrons and which subsequently diffuse over a large distance. We therefore propose that, in general, lateral charge transfer may play an essential role in imaging low-conductivity molecules by distributing the current between tip and substrate over a large sample area, thereby considerably reducing the current density.

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